GB2459509A

GB2459509A - An apparatus for casting and a method for casting

Info

Publication number: GB2459509A
Application number: GB0807614A
Authority: GB
Inventors: Stephen Roberts; Richard Stanley Goodwin
Original assignee: Goodwin PLC
Current assignee: Goodwin PLC
Priority date: 2008-04-25
Filing date: 2008-04-25
Publication date: 2009-10-28
Anticipated expiration: 2028-04-25
Also published as: DE112009001002B4; JP5282814B2; WO2009130472A1; US8056608B2; CN102015159A; GB2459509B; DE112009001002T5; GB0807614D0; CN102015159B; US20110036535A1; JP2011519313A

Abstract

An apparatus for making a metal casting, and in particular a super nickel alloy casting, comprises a mould 1 including a feeder or a riser 2, and an electrically conducting material 3 for inducing eddy currents in liquid metal in the feeder. The electrically conducting material surrounds the riser and is subject to an alternating current which causes a changing magnetic field that induces eddy currents in the liquid metal in the feeder that leads to the heating of the metal. By controlling the current, the rate of cooling of the riser can be controlled and the effects of chill off and shrinkage of the mould can be minimized. The apparatus can comprise a temperature sensor 7 for measuring the temperature of the feeder, this reading is then used to apply the appropriate strength of induced current. The feeder diameter can be greater than 150mm and the electrically conducting material can be cooled by a cooling system 4.

Description

An Apparatus for Casting and a Method of Casting The present application relates to an apparatus for casting a metal, particularly to an apparatus for making a super Ni alloy casting. The application also relates to a method of casting a metal, particularly a super Ni alloy.

An apparatus for making a casting comprises a mould defining the shape of the desired product and a feeder. A casting is where molten metal is poured into a mould which has a shape the same as or close to a desired final shape. This is different to an ingot which generally has a less complicated shape and will be subjected to further thermomechnical processing before acquiring its final shape. Molten metal is usually poured through an ingate or the feeder into the mould.

The spherical volume of the feeder is chosen so that the feeder head (i.e. the metal in the feeder) solidifies after the metal in the remainder of the mould. Usually this requires the equivalent spherical volume of the feeder to be larger than the equivalent spherical volume of the casting.

More than one feeder can be used per casting.

A riser or feeder or feeder pipe is a reservoir built into a metal-casting (sand) mould to prevent cavities due to shrinkage. Because metals are less dense as liquids than as solids, castings shrink as they cool. This can leave a void, generally at the last point to solidify. Risers prevent this by providing molten metal at the point of likely shrinkage, so that the cavity forms in the metal solidifying in the feeder, not in the casting itself.

Efficiency of feeders has previously been improved in the following ways: In a first way, insulating material is placed around the extremity of the feeder to reduce heat loss and keeping the feeder "alive" for longer. This is normally in the form of tiles or a pre formed sleeve. Also insulating powers are added to the top of feeders after pouring to also prevent heat loss.

A second way uses so called exothermics. Again, these are in the form of sleeves, which contain metal oxides which react with the molten metal on pouring and create an exothermic reaction giving extra heat to the feeder increasing solidification time.

Powders are also available which give from mild to highly exothermic reactions having the same effect. The purpose of the insulators and the exothermics is to keep the metal in the feeder liquid for longer than the metal in the casting. This is because unless the feeder head is liquid, it cannot do its job of filling any cavity left by thermal contractkn of the metal in the casting. Thermal contraction occurs both on cooling from liquid to solid metal as well as cooling from the solidus temperature down to room temperature.

With both of the above existing systems of heat loss control, efficiency of the feeder head is limited, as unless the feeder is quite big, solidification within the feeder head takes place before all of the liquid shrinkage of the casting or ingot can take place.

This is typified by the classic primary and secondary shrinkage pipe within a feeder head, and the sinking "u" shape found at the top of all conventional feeders.

Theses pipes and "u" shape show that the feeder is only providing liquid metal to the solidifying casting from the centre of the feeder, while the outer regions of the feeder, have already frozen off.

In JP 2005-329450 the temperature of a feeder head is precisely and economically controlled during casting of non ferrous metals. This is done using an indirect induction heating technique.

The non ferrous metals concerned are zinc, aluminium and magnesium. These metals have low melting points (400-700°C) and have a relatively high thermal conductivity so that a feeder diameter of 50-80mm is suitable, even for large castings.

JP 09-3 14310 discloses induction heating of molten metal in a feeder pipe to improve the yield of a casting, shorten the working time, to reduce casting defects, and to reutilise the refractory of a feeder part. The feeder of.]P 09-314310 is relatively small. The system can be used for moulding steels, aluminium alloys and zinc alloys and the example of sizes of the mould results in a product of approximately 500kg (i.e. a volume of about less than 0.2m3). A fire-proof material is provided between the coils of the induction heater and the feeder.

The present invention provides an apparatus for making a super Ni alloy casting, said apparatus comprising: a mould including a feeder; and an electrically conducting material for inducing eddy currents in metal in said feeder.

The present invention provides an apparatus for casting a metal, said apparatus comprising: a mould including a feeder; an electrically conducting material for inducing eddy currents in metal in said feeder; wherein said feeder has a diameter of greater than 150 mm.

The present invention provides an apparatus for making a casting of metal, said apparatus comprising: a mould including a feeder; and an electrically conducting material for inducing eddy currents in metal in said feeder; and a cooling system for cooling said electrically conducting material during use.

The present invention provides a method of casting a super Ni alloy comprising: pouring liquid alloy into a mould such that liquid alloy is present in a feeder of said mould; and inducing an electrical current in alloy in said feeder to reduce a rate of cooling said alloy in said feeder.

The present invention provides a method of casting an alloy comprising: pouring liquid alloy into a mould such that liquid alloy is present in a feeder of said mould; and inducing an electrical current in alloy in said feeder to reduce a rate of cooling said alloy in said feeder, wherein said feeder has a diameter of greater than 150mm.

The present invention provides a method of casting an alloy comprising: pouring liquid alloy into a mould such that liquid alloy is present in a feeder of said mould; inducing an electrical current in alloy in said feeder to reduce a rate of cooling said alloy in said feeder; and cooling an electrically conductive material used for inducing said electrical current.

The present invention will now be described by way of example only with reference to the accompanying following figures in which: Figure 1 illustrates schematically an apparatus for casting a metal according to the present invention; and Figure 2 is a perspective cutaway drawing through a valve body casting illustrating the position of an electrically conducting material for inducing eddy currents in liquid metal in a feeder.

Nickel alloys have very different feeding characteristics (i.e. behaviour in a feeder of a mould during casting) to those of steel.

The diameter of the feeders has to be limited because nickel alloys have a very low coefficient of thermal conductivity (nominally 10 W/m°C in nickel alloys compared with 50 WJm°C for steels).

If too large a diameter of feeder is used on a super nickel alloy casting then cracks will often be found under the feeder heads. This is due to the very poor thermal conductivity of the nickel alloy.

The outside of the feeder head will, as is normal, solidify first; but by the time the centre of the feeder head solidifies the outside temperature is much lower, than with a steel casting, due to the poor thermal conductivity. This means that due to the shrinkage of the metal in the centre of the feeder from just below solidification temperature to room temperature, very considerable tensile stresses are set up. This happens because, as the diameter of the outside of the feeder head and the rigidity of the outer metal become fixed but, at the same time, the metal in the centre is still cooling and shrinking. This results in very high tensile stresses which are above the ultimate tensile strength of the metal in the centre of the feeder head and therefore cracks occur.

Unfortunately during the feeder removal process, be it hot or cold process, these cracks often propagate to through wall thickness defects.

Because of the high thermal conductivity, thermal gradients required for directional solidification are difficult to control. Nickel alloys have a longer solidification range than for example steels.

Conventionally increased feeders heights are used (e.g. H:D ratio 1.5:1 to 2:1). For very large castings, shrinkage calculations often show that very large diameter feeder heads are required.

However, these are not possible because such large diameter feeder heads would result in cracking. One way to deal with this might be to provide a larger number of feeder heads at the expense of added complexity and added waste but unless the smaller heads solidify after the casting the feeder head will not do its job. Thus chill off (described below) may still be a problem.

The present invention is directed to using feeder heads with a diameter of 150-900mm or even larger. The diameter of the feeder heads is much larger than would be possible without the invention and much larger than previously used. However the large diameter is necessary in order to account for shrinkage in large super Ni alloy castings (which have not previously been possible).

Such castings may have a size of over 3000 or 6000 kg or even over 12000 kg finished weight.

This equates to a volume of at least 0.5 m3, preferably greater than 0.6 m3 or 0.7 m3 and possibly greater than 1.4 m3. The feeders may be small enough to avoid thermal shrinking induced cracking but large enough to cope with the high thermal shrinkage rates of large super Ni alloy castings. However, in some embodiments the feeders may be larger than the size at which thermal shrinking induced cracking can occur, as described below. In order to maintain alloy in the liquid phase in the feeder head for longer, an electrically conducting material is used for inducing eddy currents in the liquid metal in the feeder thereby to reduce the rate of cooling of the liquid metal in the feeder. Currents may continue to be induced in the metal in the feeder head even after solidification. This can be done as well as or instead of inducing currents in liquid metal. If currents are induced in solid metal of the feeder head, then it will be possible, as is explained below, to use a feeder head with a diameter which is larger than the critical diameter above which thermal contraction induced cracking would otherwise occur.

The control of the solidification of 150 to 900mm diameter feeder heads by induction heating and therefore improving the casting yield in super-nickel alloys with more than 30% nickel content will now be described.

As the casting solidifies liquid metal is drawn from the feeder head into the casting to reduce the amount of shrinkage in the casting. By the use of induction heating the primary feeder(s) on the casting can be kept molten for longer than normal. Secondary feeder(s) may not need to be treated in this way.

By keeping the feeder head liquid for a longer period of time it is possible to make castings, particularly but not exclusively for super Ni alloys, with a smaller feeder than is otherwise required.

This has the following beneficial effects: a) The avoidance of the need to use large diameter, full contact, feeders that end up with cracks in the middle as explained above.

b) A better yield which results in less molten metal having to be melted -at �35,000 per ton at 2008 rates, this can give significantly reduced costs.

c) The ability to make bigger super-nickel alloy castings where section thickness is greater than the normal maximum diameter feeder that can be used.

Induction heating is the non-contact heating of a metal object by electromagnetic induction, where eddy currents are generated (induced) within the metal and resistance leads to heating of the metal. An induction heater consists of an electrically conducting material, for example in the shape of a coil, through which a medium or high-frequency alternating current (AC) is passed.

The use of induction heating of feeder heads is particularly applicable to alloys containing �= 30% nickel and �=95% nickel. Typically nickel-chromium-iron, nickel-molybdenum and nickel-chromium-molybdenum alloys, together with other elements.

The use of induction heating of feeder heads allows the feeder head diameter to be smaller than would otherwise be necessary for a given size of casting. Cracking due to thermal contraction can be avoided by reducing the diameter of the feeder and/or by controlling the cooling rate of the metal at the outside of the feeder head. In the later case, the induction heating is used to reduce the temperature profile through the thickness of the feeder head as the metal in the feeder head cools. For example the outside of the feeder head has a current induced in it to slow its cooling rate so that its temperature more closely matches the temperature of the inside of the feeder head. This reduces the thermal strain induced in the feeder head by thermal contraction effects and reduces the chance of thermal cracking. As a result use of feeders with diameters with a large enough diameter for large castings are possible. The dimensions of feeder head of the present invention are given below.

Feeder diameter range: From 150mm to 900mm, preferably 300-900mm, more preferably 500-900mm. Feeder diameters larger than 900mm are also possible, particularly with controlled cooling to achieve lower thermal gradients within the feeder head.

The feeder may not be circular in cross-section. In that case the cross-sectional area of the feeder would be equivalent to the cross sectional area of a circular feeder pipe with a diameter in the above ranges.

Feeder height range: H:D ratio 1:1 to 5:1, preferably 1.25:1 to 4:1, more preferably 2:1 to 5:1 and/or preferably above about 2:5 In order to induce a current in the metal in the feeder head, an electrically conducting material is provided. Preferably the electrically conducting material is in the form of an induction coil.

The induction coil is incorporated in sand of the sand mould which is preferably used during the moulding process. Once the casting is conventionally poured a current is applied through the electrically conducting material using a power pack 5. Alternatively a separate (attached) induction coil is positioned around the feeder head and a current applied.

The induction coil is then used to control the solidification of the feeder head, allowing for longer feeder solidification times and increasing the efficiency of the feed metal. That allows big castings to solidify before the feeder head which would solidify earlier but for the induction heating. It is also used to slow the rate of cooling of the riser from solidus temperature to room temperature, thus allowing larger diameter of feeders to be used as the slow cooling will avoid a large temperature gradient across the radial diameter of the feeder.

This apparatus and method results in the following advantages: a) The ability to make larger castings in super-nickel alloys due to the reduction of the thermal limitation of riser diameter. Otherwise castings of this size could not be made.

b) Improved yield.

c) Less expensive molten metal used.

d) Reduced amount of returned metal.

e) Less energy required.

f) Quicker feeder removal because of the reduced diameter.

g) Lower cooling gradient across the feeder radial diameter.

Figure 1 is a schematic view of a casting 1. The apparatus for making the casting 1 comprises a mould which defines the desired shape of the casting 1. A feeder is also provided in the mould.

Liquid metal is poured into the mould through an ingate 6 or the feeder. The mould is filled to a level such that metal fills the feeder to near its top. During solidification and thereby contraction of the casting 1, liquid metal from the feeder head 2 will move into the casting under hydrostatic pressure so that the casting is as close to the desired shape as possible and so that no shrinkage voids due to thermal contraction are formed. As can be seen from figure 2, the mould preferably comprises an ingate 6 which is used to provide liquid metal to the mould. The ingate 6 is in the form of a pipe which leads from about the top level of the feeder to the bottom of the mould so that liquid metal fills the mould from the bottom. A metal plate or similar may be placed at the bottom of the mould in order to chill the liquid metal so that solidification starts from the bottom of the mould furthest from the feeder head 2.

The mould also includes an electrically conducting material 3. This is also illustrated in Figure 1 (it is the only part of the apparatus which is illustrated in Figure 1). In the preferred embodiments the electrically conducting material 3, which is for inducing any currents in liquid metal in the feeder (i.e. liquid metal which forms the feeder head), is in the shape of a coil. However, other shapes may be suitable.

The electrically conductive material may be embedded in material of the mould. For example, if the mould is a sand mould then the electrically conductive material can be embedded into the sand during shaping of the sand into the desired shape of the mould. Alternatively, the electricaiiy conductive material can be placed around the refractory material forming a feeder and thereby not be embedded in the mould.

Because of their low thermal conductivity super Ni alloy castings take a long time to solidify. This provides particular challenges for the mould. In particular, the refractory material of the mould may become very hot. Indeed, it is possible for the electrically conducting material 3 used for inducing eddy currents in the liquid metal in the feeder to reach its own metal point. For this purpose a cooling system 4 is provided for cooling the electrically conducting material during use.

One way of providing for this is to pass a heat transfer fluid through, around or close to the electrically conducting material 3. One way of doing this is to provide the electrically conducting material 3 in the form of a tube and to pass the cooling fluid (liquid or gas) through the tube.

Some induction furnaces use a hollow induction coil through which cooling liquid (usually water) is passed. However, in the present invention preferably a cooling gas is used rather than water.

This is because there is a danger as water and molten metal can lead to an explosion, which would occur if the coil melted whilst there was still molten metal in the mould, gas is a far preferable cooling medium. Therefore the use of a gas as the heat transfer fluid for taking heat away from the electrically conducting material is preferred. The cooling gas might be an inert (pure) gas such as nitrogen or argon, or could be a mixture of gasses (for example air) or could be a refrigerant gas.

In the cooling system 4 cold heat transfer fluid is pumped in at one end of the electrically conducting material in the mould. The heat transfer fluid heats up as it passes the electrically conducting material. At the other end of the electrically conducting material the heat transfer fluid is removed at which point it is at a higher temperature than when it first came into contact with the electrically conducting material. The heat transfer fluid can then either be disposed of or can be recycled in which case it will need to be cooled prior to being pumped back through, around or close to the electrically conducting material to perform its cooling task.

Many variations of cooling system are possible. For instance, it is not necessary for the cooling fluid to pass all the way along the electrically conducting material. For instance, the electrically conducting material could be split into several lengths each of which are part of an independent cooling system.

In an embodiment the coil could be made out of a higher temperature melting point metal that would add to the safety and robustness of the coil.

Now a description will be given of how the apparatus for making a casting is used.

The casting is conventionally poured, with an induction coil (moulded) in position around the feeder head. The radial distance from the feeder edge is between 10 and 300 mm, preferably between 40 and 10 mm, most preferably about 75mm.

The induction coil 3 is then used to control the solidification of the feeder head, allowing for longer feeder solidification times and increasing the efficiency of the feed metal. When a feeder head (also known as a riser) has a smaller mass than the section of the casting it is feeding it will chill off and fail to do its job.

The criteria for an effective feeder is that i) it does not chill off and ii) it has enough volume to overcome the volume shrinkage in the casting.

a) In the first, approximately, 10 minutes after pouring the induction coil 3 is not energised but it does have a cooling media (gas or liquid) continuously circulated through it to prevent the induction coil from melting.

b) After the first, approximately, 10 minutes the induction coil is energised with a local induction melting furnace power pack 5 and the temperature of the feeder sitting within the coil 3 is kept molten for the period that the ultimate cast shape of the casting takes to solidify.

After this time has elapsed the induction can be de-energised but the cooling medium must be kept flowing through the coil for a considerable time (hours) until such time as the radiated and conducted heat can no longer melt the coil.

Therefore, the casting yield is improved allowing a sound casting to be produced with a dramatically reduced poured weight.

The idea is to utilise a greater proportion of the feeder's volume as useful feed metal, rather than only a portion of the feeder being valuable as genuine feed metal. That is, the so called yield (the ratio of weight of metal which makes up the casting to weight of metal which makes up the casting and the feeder head) of the casting can be increased. Complex castings can result in a yield of 30% or less. With the present invention, because smaller feeder heads can be used, a yield of greater than 50% can be achieved in some circumstances on complex castings.

As can be seen from figure 2, a casting may include more than one feeder head 2 as well as an ingate 6. As can be seen, the size of the feeder heads is great so that the feeder heads solidify after the casting. The present invention allows smaller feeder heads to be utilised.

With the induction heating system, much more of the feeder's volume of metal can be utilised as solidification is controlled so that the casting has almost solidified itself before the feeder is allowed freeze. That is, because solidification of the feeder head can be controlled, piping in the feeder (where the outside of the feeder solidifies first and liquid metal in the centre of the feeder flows downwards leaving a cavity in the top middle of the feeder head) can be avoided. This is done by maintaining the outside of the feeder head liquid for longer than would occur without the induction heating. This can result in a flat feed which is a feeder head which is cylindrical without piping.

A flat feed can be achieved, or a feeder head of a diameter larger than that which would be possible without thermally induced cracking can be used if induction heating is used. A thermocouple 7 can provide information about the temperature of the outside of the feeder head and this information can be used in a feedback or feedforward manner by a controller of the power pack 5 to induce enough current in the feeder head (particularly in the outside of the feeder head) to keep the temperature of the outer surface of the feeder head liquid. Once solidification has taken place, the same or a similar control loop can be used to ensure a near uniform temperature profile (radially) though the feeder head 2 during cooling to room temperature. This can also be important because during cooling from the solidus (about 1400C) to room temperature it is still possible for thermally induced cracking to occur. Therefore the controller of the induction heater can continue to control the temperature of the outer surface of the feeder head during cooling (reduce its cooling rate) and thereby larger diameter feeder heads 2 than could otherwise be used can be used with the present invention.

A further benefit to the system is the ability to keep the feeder head "alive" for longer which then can enable further topping up of the head with metal.

Claims

CLAIMS1. An apparatus for making a super Ni alloy casting, said apparatus comprising: a mould including a feeder; and an electrically conducting material for inducing eddy currents in metal in said feeder.
2. The apparatus of claim 1 wherein said feeder has a diameter of greater than 150 mm.
3. The apparatus of claim 2 wherein said feeder has a diameter of greater than 300mm, preferably greater than 500mm.
4. The apparatus of any one of claims 1-3, wherein said mould has a volume of greater than O.5m3, preferably greater than O.6m3, more preferably greater than O.7m3.
5. The apparatus of any one of the preceding claims, wherein a ratio of the height to the diameter of said feeder is in the range of 1:1 to 5:1, preferably 1.25:1 to 4:1.
6. The apparatus of any one of the preceding claims, further comprising a cooling system for cooling said electrically conducting material during use.
7. The apparatus of any claim 6, wherein said cooling system uses a gas as a heat transfer fluid for removing heat from said electrically conducting material.
8. The apparatus of any one of the preceding claims, comprising a plurality of feeders.
9. The apparatus of any one of the preceding claims, wherein said mould further comprises an ingate for the introduction of liquid metal into said mould.
10. The apparatus of any one of the preceding claims, further comprising a controller, in use, for controlling the current induced in said liquid metal and thereby to control the cooling rate of metal in said feeder.
11. The apparatus of claim 10, further comprising a sensor for sensing the temperature of metal in said feeder and said controller controls the current induced by said electrically conducting material based on the temperature measured by said sensor,
12. The apparatus of claim 11, wherein said sensor is for measuring the temperature of metal in a radially outer portion of said feeder.
13. An apparatus for casting a metal, said apparatus comprising: a mould including a feeder; an electrically conducting material for inducing eddy currents in metal in said feeder; wherein said feeder has a diameter of greater than 150 mm.
14. The apparatus of claim 13, wherein said diameter of said feeder is greater than 300mm, preferably greater than 500mm.
15. The apparatus of claim 13 or 14, wherein said mould has a volume of greater than O.5ni3, preferably greater than O.6m3, more preferably greater than 0.7m3.
16. The apparatus of any one of claims 13,l4and 15, wherein a ratio of the height to the diameter of said feeder is in the range of 1:1 to 5:1, preferably 1.25:1 to 4:1.
17. The apparatus of any one of claims 13-16, further comprising a cooling system for cooling said electrically conducting material during use.
18. The apparatus of claim 17, wherein said cooling system uses a gas as a heat transfer fluid for removing heat from said electrically conducting material.
19. The apparatus of any one of claims 13-18, wherein said mould comprises a plurality of feeder heads.
20. The apparatus of any one of claims 13-19, wherein said mould further comprises an ingate for the introduction of liquid metal into said mould.
21. The apparatus of any one of claims 13-20, further comprising a controller, in use, for controlling the current induced in said liquid metal and thereby to control the cooling rate of metal in said feeder.
22. The apparatus of claim 21, further comprising a sensor for sensing the temperature of metal in said feeder and said controller controls the current induced by said electrically conducting material based on the temperature measured by said sensor.
23. The apparatus of claim 22, wherein said sensor is for measuring the temperature of metal in a radially outer portion of said feeder.
24. The apparatus of any one of claims 13-23, wherein said apparatus is for making a super Ni alloy casting.
25. An apparatus for making a casting of metal, said apparatus comprising: a mould including a feeder; and an electrically conducting material for inducing eddy currents in metal in said feeder; and a cooling system for cooling said electrical'y conducting material during use.
26. The apparatus of claim 25, wherein said cooling system uses a gas as a heat transfer fluid for removing heat from said electrically conducting material.
27. The apparatus of claim 25, wherein said cooling system uses a liquid as a heat transfer fluid for removing heat from said electrically conducting material.
28. The apparatus of claim 27, wherein said liquid is water or other liquid.
29. The apparatus of any one of claims 25-28, wherein said feeder has a diameter of greater than 150mm.
30. The apparatus of claim 29, wherein said feeder head has a diameter of greater than 300mm, preferably greater than 500mm.
31. The apparatus of any one of claims 25-30, wherein said mould has a volume of greater than O.5m3, preferably greater than 0.6m3, more preferably greater than O.7m3.
32. The apparatus of any one of claims 25-31, wherein a ratio of the height to the diameter of said feeder is in the range of 1:1 to 5:1, preferably 1.25:1 to 4:1.
33. The apparatus of any one of claims 25-32, wherein said mould has a plurality of feeders.
34. The apparatus of any one of claims 25-33, wherein said mould further comprises an ingate for the introduction of liquid metal into said mould.
35. The apparatus of any one of claims 25-34, further comprising a controller, in use, for controlling the current induced in said liquid metal and thereby to control the cooling rate of metal in said feeder.
36. The apparatus of claim 35, further comprising a sensor for sensing the temperature of metal in said feeder and said controller controls the current induced by said electrically conducting material based on the temperature measured by said sensor.
37. The apparatus of claim 36, wherein said sensor is for measuring the temperature of metal in a radially outer portion of said feeder.
38. The apparatus of any one of claims 25-37, wherein said apparatus is for making a super Ni alloy casting.
39. A method of casting a super Ni alloy comprising: pouring liquid alloy into a mould such that liquid alloy is present in a feeder of said mould; and inducing an electrical current in alloy in said feeder to reduce a rate of cooling said alloy in said feeder.
40. The method of claim 39, wherein said feeder has a diameter of greater than 150mm, preferably greater than 300mm, more preferably greater than 500mm.
41. The method of claim 39 or claim 40, wherein at least 3 tonnes of liquid alloy, preferably at least 6 tonnes of liquid alloy, is poured through said feeder.
42. The method of claim 39, 40 or 41, wherein a ratio of the height to the diameter of said feeder is in the range of 1:1 to 5:1, preferably 1.25:1 to 4:1.
43. The method of any one of claims 39-42, further comprising cooling electrically conducting material used for inducing said electrical current.
44. The method of claim 43, wherein said cooling comprises transferring heat from said electrically conducting material using a gas.
45. The method of claim 43, wherein said cooling comprises transferring heat from said electrically conducting material using liquid.
46. The method of any one of claims 39-45, wherein said pouring liquid alloy through a feeder comprises pouring liquid alloy through a plurality of feeders.
47. The method of any one of claims 39-45, wherein said pouring comprises pouring liquid metal into said mould through an ingate.
48. The method of any one of claims 39-47, further comprising controlling the current induced in said liquid metal and thereby to control the cooling rate of metal in said feeder based on the temperature of metal in said feeder.
49. The method of claim 48, wherein said temperature of metal in said feeder is the temperature of metal in a radially outer portion of said feeder.
50. A method of casting an alloy comprising: pouring liquid alloy into a mould such that liquid alloy is present in a feeder of said mould; and inducing an electrical current in alloy in said feeder to reduce a rate of cooling said alloy in said feeder, wherein said feeder has a diameter of greater than 150mm.
51. A method of casting an alloy comprising: pouring liquid alloy into a mould such that liquid alloy is present in a feeder of said mould; inducing an electrical current in alloy in said feeder to reduce a rate of cooling said alloy in said feeder; and cooling an electrically conductive material used for inducing said electrical current.
52. A method substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.
53. An apparatus substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.